Chips made of extremely thin silicon could go into your body to kill bacteria or deliver drugs and then dissolve harmlessly when they're done. They could also open up new possibilities in espionage.

Researchers from Tufts, Northwestern, and the University of Illinois at Urbana-Champaign have pulled off a disappearing act for electronic devices that could change the way we think of our gadgets, as well as introduce new capabilities for medical implants and even spy gear.

The technology, which will be announced in a paper this week in Science, is called transient electronics or resorbable electronics. These systems work until they are no longer needed, at which point they dissolve completely away—the dissolution triggered by ordinary water in their operating environment. The most immediate application envisioned by the developers is for medical devices that dissolve in the human body a set period of time after surgeons implant them.

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"This is a completely new concept," said Yonggang Huang, who leads the theory, design, and modeling team for the project at Northwestern University, in a statement released by the university.

The new electronics are silicon-based, just like conventional electronics. The trick to getting them to dissolve in water is to make the silicon extremely thin, according to John Rogers, the University of Illinois at Urbana-Champaign professor who heads up the project. "Silicon dissolves at a rate of about 1 nanometer per day in the body," Rogers tells PM. For a standard integrated circuit wafer, says Rogers, dissolution would take 1000 years. But a 20-nanometer-thick silicon chip, the size that the researchers created, can disappear in just a couple of weeks.

The researchers formed the wires and other metal parts needed to create electronic devices from magnesium, a bio-friendly metal already used in medical devices such as stents. Magnesium has the added benefit of also dissolving in water, and here, too, thin components make the disappearing act possible. For power the devices rely on induction coils rather than potentially toxic, nonresorbable batteries.

The chip is covered by magnesium oxide, along with an outer jacket of silk—whose dissolving properties in the human body are well understood because of applications such as silk sutures. Altogether, the system becomes a kind of time-release capsule, and the thickness of the covering determines how quickly bodily fluids will begin dissolving the chip. The team created demo devices that dissolve in anywhere from the two weeks allowed by a bare chip to six months or longer in thick jackets.

So far the team has created components such as transistors, resistors, diodes, and strain sensors. An immediate use for these devices could be to kill bacteria by heating a specific region within the body. Other resorbable electronics could include pacemakers, temperature monitors, or drug delivery systems. The benefit to a patient is that only one surgery is required. There's no need for a second surgery to remove the components, and the fact that they dissolve cuts the risk of long-term complications from leaving them in place.

The work is being funded in part by DARPA, the Defense Department's mad science arm, which sees a range of applications. To no one's surprise, though, those uses are classified."I can't get into those details," he tells PM. "You can think about it yourself."

It's not hard to imagine the uses of small electronic devices that vanish without a trace when exposed to water. Disappearing sensors and other spy gear could be air-dropped or strategically embedded in hostile environments with no one the wiser.

Among civilian uses outside the medical field, Rogers says transient electronics could be used in monitoring large chemical spills. "Maybe a scenario would be that you drop 100,000 of these things out of an airplane, distribute them across a spill site, and have sensor-plus-wireless-communication capabilities embedded in those devices so you can monitor in real time the spatial and temporal changes in the spill." Power in such devices would likely come from tiny solar cells or radio waves beamed at them. After the spill has been cleaned up, the devices would dissolve harmlessly rather than creating their own cleanup problem.

The same could be true for consumer electronics. "The lifecycle of technologies these days in the consumer world is pretty short," Rogers says. "It might be interesting to have devices that last for a year or two and then at that point kind of resorb in a landfill or more generally in the environment, without associated waste streams."

Michael Belfiore is the author of The Department of Mad Scientists: How DARPA Is Remaking Our World, from the Internet to Artificial Limbs and is a frequent contributor to Popular Mechanics.